Liverpool and Dortmund were paired together in the Europa League quarter-finals and the highly-anticipated first-leg encounter will take place in Germany this week.
Klopp, now in charge of the Reds, will be returning to his former club for the first time since leaving the club after a highly successful period which included two Bundesliga title triumphs.
Speaking ahead of the encounter, Dortmund chief Watzke says he already has fears of happy reunion with Klopp and urges his side’s supporters to put past feelings aside until after the tie is over.
“I am afraid that Klopp is trying to lull us, that he will draw the fans on his side which will create a friendly atmosphere. There must not be an amicable reunion. We are very clear opponents,” he told Bild.
“My message to the fans is that we have sympathy expressions to our former coach only after the game, not previously. That would be the biggest mistake we can make.”
Dortmund is renowned across Europe for creating a hostile atmosphere and the Yellow Wall - the standing section of fans behind the goal - often plays a key role in their team’s home encounters.
A friendly atmosphere towards Klopp could well give Liverpool an advantage, and as such Watzke is understandably imploring the club’s fans to put past feelings aside until after the match.
The Reds reached the Europa League quarter-finals following a 3-1 aggregate win over Manchester United while Dortmund beat Tottenham Hotspur both home and away in the previous round.